This invention relates to a method of manufacturing austenitic stainless steel plates.
As is well known in the art, stainless steel has excellent corrosion proofness and heat resistant property, and depending upon its composition it is classified into austenite type, ferrite type and duplex of austenite and ferrite. Of these types, most of the stainless steels are limited to SUS 304 and 316 which are of the austenite type. These types of austenitic stainless steel are used as corrosion resistant material, heat resistant material, structural nonmagnetic plates, and low temperature steel plates. In recent years, these steels are used as clad steel in combination with low alloy steel.
In the prior art, it has been recognized that the austenitic stainless steel is subjected to a solution treatment. The purpose of this treatment is (1) to completely convert carbide and nitride into a solid solution and then to quench so that the carbide and nitride would not precipitate during succeeding cooling step, and (2) to eliminate strain and nonuniform structure caused by hot rolling. However, the solution treatment is not suitable to save energy because the solution treatment requires reheating and quenching on the outside of a production line. Moreover, a range in which thick plate can be manufactured is limited due to heat treatment furnace. Furthermore, SUS 304 and 316 have low yield strength which limits the range of use of thick stainless steel plates as structural materials.
Regarding SUS 304 and 316, for the purpose of widening the range of use, the quantities of additional elements have been increased which have suceeded to increase more or less the strength, but this measure increases manufacturing cost so that it does not provide fundamental solution.